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Q: Are plaster, stucco and EIFS the same?
A: While there are several parts of the North
America where stucco always has a strong presence, there appears
to be a general renewed interest in portland cement plaster for
building finishes everywhere. We are often asked if stucco and plaster
are the same thing, and if plaster and EIFS are the same thing.
 The
answer requires a thorough explanation. Plaster is the general term
for material that is applied to a wall surface in a thin layer.
Portland cement-based plaster is such a material that uses portland
cement as the binder. It is sometimes called “traditional
stucco.” Stucco is a somewhat colloquial term for portland
cement plaster, and some people consider it to refer to an exterior,
not interior, finish. EIFS stands for exterior insulation and finish
system, which is sometimes (incorrectly) called “synthetic”
stucco. To complicate matters, “plastering” is the verb
that describes the action of applying any of these various materials
to a wall surface.
 Portland
cement plaster is applied either by hand or machine to exterior
and interior wall surfaces in two or three coats. It may be applied
directly to a solid base such as masonry or concrete walls, or it
can be applied to metal lath attached to frame construction, solid
masonry, or concrete construction. Applied directly to concrete
masonry, portland cement plaster provides a tough 1/2-in. thick
facing that is integrally bonded to the masonry substrate. When
applied to metal lath, three coats of plaster form a 7/8- in. total
thickness. A vapor permeable, water-resistant building paper separates
the plaster and lath from water-sensitive sheathing or framing.
Portland cement plaster has high impact resistance and sheds water,
but breathes, allowing water vapor to escape. It’s a proven
system that works in all climates.
EIFS consists of a polymer-based laminate that is wet-applied,
usually in two coats, to rigid insulation board that is fastened
to the wall with adhesive, mechanical fasteners, or both. Polymer
based (PB) systems, sometimes known as thin coat, soft coat, or
flexible finishes, are the most common. The basecoat for PB systems
is usually 1/16 in. thick and finish coat thickness is typically
no thicker than the maximum sand particle size in the finish coat.
EIFS experienced performance problems in the 1990s, including water
leakage and low impact resistance. While the PB skin repels water
very effectively, problems arise when moisture gets behind the skin—typically
via window, door, or other penetrations—and is trapped inside
the wall. Trapped moisture eventually rots insulation, sheathing,
and wood framing. It also corrodes metal framing and metal attachments.
There have been fewer problems with EIFS used over solid bases such
as concrete or masonry because these substrates are very stable
and are not subject to rot or corrosion.
Clearly, portland cement plaster should not be confused with the
exterior insulation and finish systems. The systems may share similarities
in application techniques or final appearance, but they systems
perform differently in resisting weather, especially wet conditions.
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